This invention relates to a method for refining, reclaiming or reradiating glyceride oils, fatty chemicals and wax esters by contacting them with an adsorbent capable of removing certain impurities. The method has been designated "MPR", which may refer to modified physical refining, modified physical reclamation or modified physical remediation. MPR is intended to refer to any treatment of glyceride oils, fatty chemicals or wax esters according to the procedures of the invention described herein, regardless of the stage of refining, use or re-use of the composition being treated. MPR will be useful in treating these materials whether they are intended for food-related or for non-food-related applications.
The MPR method combines the benefits of caustic treatment and physical adsorptive treatment, while eliminating the key disadvantages of each process. It previously had been found that amorphous silicas are made more effective in adsorbing phospholipids from caustic treated or caustic refined glyceride oils by the presence of soaps in the oils. It now has been discovered that the addition of only very minor amounts of caustic creates sufficient, though small, quantities of soap to enhance phospholipid adsorption on amorphous silica.
For purposes of this specification, the term "impurities" refers to soaps and phospholipids. The phospholipids are associated with metal ions and together they will be referred to as "trace contaminants." The term "glyceride oils" as used herein is intended to encompass both vegetable and animal oils. The term is primarily intended to describe the so-called edible oils, i.e., oils derived from fruits or seeds of plants and used chiefly in foodstuffs, but it is understood that oils whose end use is as non-edibles are to be included as well. In addition, the process of this invention may be used with other fatty chemicals and wax esters where phospholipids and associated metal ions are contaminants which must be removed.
The presence of phosphorus-containing trace contaminants can lend off colors, odors and flavors to the finished oil product. These compounds are phospholipids, with which are associated ionic forms of the metals calcium, magnesium, iron and copper. For purposes of this invention, references to the removal or adsorption of phospholipids is intended also to refer to removal or adsorption of the associated metal ions.
In the preferred embodiment of this invention, the terms "glyceride oil," "crude glyceride oil," "degummed oil," "caustic refined oil," "oil" and the like as used herein refer to the oil itself, including impurities and contaminants such as those discussed in this specification. These are substantially pure oils at about 99.8% or higher oil content, with respect to solvents (Handbook of Soy Oil Processing and Utilization, pp. 55-56 (1980)). That is, the glyceride oils utilized in the preferred embodiment are substantially pure oils, in the complete absence or substantially complete absence of solvents such as hexane. Notwithstanding this purity with respect to solvents, it will be understood that the oils do contain contaminants, such as phosphorus, free fatty acids, etc., as described in detail below. Similarly, fatty chemicals and wax esters preferably are treated in substantially pure states, in the complete or substantially complete absence of solvents. In these preferred embodiments, the method of this invention can be categorized as non-miscella refining, remediation or reclamation.
This contrasts to solvent/oil solutions, or miscella as referred to by the industry. The initial oil extraction process in which oils are removed from seeds typically is done by solvent extraction (e.g., with hexane). The result is a solvent/oil solution which may be 70-75% solvent. Refining methods which utilize this solution commonly are referred to as miscella refining. In an alternative embodiment, the methods of this invention can be applied to miscella refining, remediation or reclamation. This conveniently may take place immediately after solvent extraction, for miscella refining. Alternatively, solvent/oil solution may be prepared at any stage of refining or use, for miscella refining, remediation or reclamation. All descriptions contained herein which are directed to non-miscella processing may be applied as well to solvent/oil miscella.
With respect to initial refining applications, crude glyceride oils, particularly vegetable oils, are refined by a multi-stage process, the first step of which typically is "degumming" or "desliming" by treatment with water or with a chemical such as phosphoric acid, malic acid, citric acid or acetic anhydride, followed by centrifugation. This treatment removes some but not all gums and certain other contaminants. Some of the phosphorus content of the oil is removed with the gums.
Either crude or degummed oil may be treated in a traditional chemical, or caustic, refining process. The addition of an alkali solution, caustic soda for example, to a crude or degummed oil causes neutralization or substantial neutralization of free fatty acids ("FFA") to form alkali metal soaps. In traditional caustic refining, an excess of caustic over FFA is added to ensure that neutralization of all or substantially all FFA takes place. The following equation, used where the caustic is lye, is used to calculate the amount of caustic solution to be added ("wt% lye"), which varies with the FFA content and with the concentration of the caustic ("% NaOH in solution"): ##EQU1## (Handbook of Soy Oil Processing and Utilization, pp. 90-91 (1980)). The term "% excess NaOH" refers to a mathematical excess selected to ensure neutralization of FFA; typically this is at least 10% (entered into the equation in decimal form as "0.1").
This neutralization step in the traditional caustic refining process will be referred to herein as "caustic treatment" and oils treated in this manner will be referred to as "caustic treated oils"; these terms will not be used herein to refer to the small quantities of caustic added in the MPR process of this invention. The large quantity of soaps (typically at least 7500-12,500 ppm) generated during traditional caustic treatment is an impurity which must be removed from the oil because it has a detrimental effect on the flavor and stability of the finished oil. Moreover, the presence of soaps is harmful to the acidic and neutral bleaching agents and catalysts used in the oil bleaching and hydrogenation processes, respectively.
Prevalent industrial practice in traditional caustic refining is to first remove soaps by centrifugal separation (referred to as "primary centrifugation"), followed by a water wash and second centrifuge. The waste from this first centrifuge is frequently acidulated to produce FFA, which is removed. The remaining acidified water requires costly disposal. Additionally, this step is responsible for high neutral oil loss ("NOL") due to entrainment of oil in the soap phase. Generally, the primary centrifugation is followed by water wash and a second centrifugation in order to reduce the soap content of the oil below about 50 ppm. The water-washed oil then must be dried to remove residual moisture to below about 0.1 weight percent. The dried oil is then either transferred to the bleaching process or is shipped or stored as oncerefined oil.
A significant part of the waste discharge from the caustic refining of vegetable oil results from the centrifugation and water wash process used to remove soaps. In addition, in the traditional caustic refining process, some oil is lost in the water wash process. Moreover, the dilute soapstock must be treated before disposal, typically with an inorganic acid such as sulfuric acid in a process termed acidulation. Sulfuric acid is frequently used. It can be seen that quite a number of separate unit operations make up the soap removal process, each of which results in some degree of oil loss. The removal and disposal of soaps and aqueous soapstock is one of the most considerable problems associated with the caustic refining of glyceride oils.
An improved, or modified, caustic refining process is taught in European Patent Publication No. 0247411. This modified caustic refining ("MCR") process removes soaps and phospholipids from caustic treated or caustic refined oils in a single unit operation by adsorption of these contaminants onto amorphous silica. The water wash centrifuge steps are eliminated, along with the waste streams and NOL associated with those steps. However, in MCR, as in traditional caustic refining, very large quantities of soaps still are generated by neutralization of free fatty acids. The present MPR process seeks to advance the art further by reducing initial soaps, adsorbent loadings and NOL as compared with the previous MCR process.
An additional consequence of the formation and removal of large quantities of soaps in traditional or modified caustic refining processes is that significant amounts of natural antioxidants (e.g., tocopherol) are removed with the soaps. This is detrimental to the oil, reducing its oxidative stability. Moreover, valuable vitamins (such as vitamin A in fish oils) may also be lost in the soap removal process.
Alternatively, oil may be treated by traditional physical refining. A primary reason for refiners' use of the physical refining process is to avoid the wastestream production associated with removal of soaps generated in the caustic refining process: since no caustic is used in physical refining, no soaps are generated. Following degumming, the oil is treated with one or more adsorbents to remove the trace contaminants, and to remove color, if appropriate. Physical refining processes do not include any addition of caustic and no soaps are generated. Although physical refining does eliminate problems associated with soap generation in caustic refining, quality control in physical refining processes has proven difficult, particularly where clays are used as the adsorbent. In addition, large quantities of clay adsorbents are required to achieve the low contaminant levels desired by the industry and there is considerable neutral oil loss associated with use of such large quantities of clay.
U.S. Pat. No. 4,629,588 (Welsh et al.) discloses a physical adsorption process in which amorphous silica adsorbents are used to remove trace contaminants from glyceride oils. The Welsh process is particularly effective when the phospholipids present in the oil are in hydratable form. The process is less effective in treating oils which have been dried (e.g., for storing), in which the phospholipids have been dehydrated to a more difficult-to-remove form.